Numerous actuators are used in a motor vehicle. The actuators usually encompass an electric-motor drive system, a linkage, and an actuating member whose position can be adjusted by the electric motor and via the linkage. Such actuators are used, for example, as throttle valve adjusters, as exhaust gas recirculation valves, for charge swirl flaps, and numerous comparable components.
Depending on the area of application, such actuators are often equipped with a position sensor to read back the actual position of the actuator. A position sensor of this kind can be used on the one hand to check the correct position of the actuating member. It is thereby possible to monitor whether the commanded position of the actuator also corresponds to the actual actuated position of the actuating member. On the other hand, with the aid of the actual position sensed by the position sensor, it is possible to carry out closed-loop position control of the actuating member, by controlling in closed-loop fashion the measured actual position as compared with a predefined target position.
Brush-commutated electric motors are usually used for such actuators. These motors have the disadvantage, however, that they exhibit degraded EMC characteristics due to the production of brush sparking. They furthermore have higher energy consumption, for example because the brushes rub against the commutator, and have a reduced service life because of the wear on the brushes.
These disadvantages do not apply to electronically commutated (brushless) electric motors. The latter do, however, require external commutation, which requires a knowledge of the rotor position. The usual methods for sensing rotor position use additional rotor position sensors in the electric motor, which make the actuator as a whole more expensive and moreover increase the wiring complexity between the actuator and a corresponding control unit. Sensorless methods, which are based, e.g., on a measurement of the voltage induced in the stator winding, also require complex circuitry in the control unit, and generally are too complex for use in an actuator.
Alternative methods, in which the rotor position is determined via a measurement of the rotor position-dependent inductance of the stator coils, likewise require complex circuitry in the control unit and in addition are not as robust and reliable as the sensor-based methods for measuring rotor position.
It is therefore an object of the present invention to provide an actuator, having an electronically commutated electric motor, that can be realized in simple fashion and does not exhibit the above disadvantages.